The present invention relates to an apparatus for humidifying polished rice and to a rice milling system comprising the apparatus and a rice polishing machine.
During polishing of brown rice by a rice polishing machine to form polished rice, heat is generated to take moisture away from the rice, resulting in deterioration of the taste of cooked rice. Generally, therefore, the polished rice is humidified after having been polished by the rice polishing machine. Specifically, the rice after having been polished is charged into a tank of a humidifying apparatus. Moisture is added to the polished rice by the humidifying apparatus slowly at a rate of the order of 0.2% to 0.3% per hour for a period of time of five (5) to ten (10) hours, in order to prevent abrupt absorption of moisture from causing cracks to be formed in the polished rice. In this manner, the polished rice is finished to one having a moisture content of about 14% to 15% which is adequate for rice to be cooked by boiling. That is to say, it is now essential to humidify the rice after having been polished, because of a recent tendency that a producer delivers brown rice which is dried slightly excessively, and because of a demand for tasty rice from consumers.
The above-described humidifying apparatus is known from Japanese Patent Application Laid-Open No. Sho 60-25548 filed by the same applicant as this application. The humidifying apparatus is arranged between a plurality of rice polishing machines, to form a rice processing line or a rice milling system. The humidifying apparatus comprises an air supply chamber and an air discharge chamber which are arranged respectively on one and other sides of the tank. A plurality of air supply passages communicating with the air supply chamber and a plurality of air discharge passages communicating with the air discharge chamber are arranged within the tank one over another alternately and in a zigzag fashion. The tank is formed at its bottom with a discharge port to which a discharge pipe is connected. A recirculation passage has one end thereof connected to the discharge pipe and the other end connected to the tank. A selector valve is arranged at the connection between the discharge pipe and the one end of the recirculation passage. Polished rice is recirculated through the tank by the recirculation passage while being humidified, so that the polished rice is humidified and is brought to a predetermined moisture content. In this case, a moisture absorption rate does not exceed 0.2% to 0.3% per hour. Accordingly, about five (5) hours are required to raise the moisture content of the polished rice by 1%. This results in lowering of a serviceability ratio of the rice milling system.
In the recent rice milling system, various instruments or equipments having their respective large processing capacities are arranged in series, and efficient operation is carried out by these equipments. Since, however, the step of humidifying the polished rice takes five to ten hours as described above, the humidification step interrupts continuous flow of the entire steps of the system. In addition, the humidification requires the tank of large capacity.
Further, the rate of absorption of moisture of the polished rice differs from part to part of the polished rice grain. Specifically, the back side of the polished rice grain is difficult to absorb moisture, while the front side is easy to absorb moisture. Accordingly, if moisture adheres to the polished rice grain in a one-sided fashion when the polished rice is tempered, cracks are formed in the rice grain because of a difference in rate of moisture absorption.